The invention relates to vestigial sideband (VSB) signal receivers and, more particularly, the invention relates to timing recovery circuits for such VSB receivers.
A conventional vestigial sideband (VSB) signal receiver for a high definition television (HDTV), as described in the xe2x80x9cGuide To The Use Of The ATSC Digital Television Standardxe2x80x9d Document A/54, Advanced Television Systems Committee, pp. 110-111, Apr. 12, 1995 which is incorporated herein in its entirety by reference, contains an analog circuit to perform carrier recovery. The conventional carrier recovery process uses a frequency locked loop (FLL) and a phase lock loop (PLL) that cooperatively operate to lock onto a pilot carrier of the VSB signal. The recovered carrier signal is then used to produce the in-phase and quadrature components of the VSB signal. Once the VSB signal components are recovered, the in-phase (I) component is digitized and then digitally processed to recover symbol timing and decode the data transmitted within the VSB signal.
Symbol timing recovery is performed using the digitized I component only. To accomplish accurate timing recovery using only the I component, the timing recovery circuitry of the VSB signal receiver must detect a four symbol segment synchronization header within the data of the VSB signal. The synchronization header is used to synchronize the receiver symbol timing with the received signal such that the symbols can be accurately decoded to recover the data transmitted within the VSB signal. Consequently, current VSB receivers must have analog circuitry to perform certain functions prior to digitization of the signal and must utilize synchronization header information to achieve accurate symbol timing. The use of analog circuitry is prone to add noise to the received signal and the processing required for decoding the synchronization header is an inefficient use of the receiver.
Therefore, there is a need in the art for a digital passband carrier and timing recovery circuit that performs carrier recovery and symbol timing recovery upon a VSB signal to recover the in-phase and quadrature-phase components of the VSB signal.
The disadvantages associated with the prior art are overcome by the invention of a method and apparatus for performing phase detection and timing recovery for a vestigial sideband (VSB) signal by processing a complex valued passband VSB signal using a high order non-linearity to detect the phase of the VSB signal. The non-linearity is produced by extracting the complex bandedge signals from a VSB signal and multiplying the complex conjugate of the lower bandedge signal with the upper bandedge signal using a complex multiplier. The real and imaginary components of the output of the complex multiplier are then multiplied with one another using a real multiplier. The result is a phase error signal that is used as a control signal for a numerically controlled oscillator. The non-linearity can be mathematically defined as:
v(t)=g+(t)xc3x97gxe2x88x92*(t)
y(t)=sgn(Re {v(t)})xc3x97Im{v(t)}
where y(t) is the is the output (phase error signal) of the phase detector, g+(t) is the complex upper (positive frequency) bandedge signal, gxe2x88x92*(t) is the complex conjugate of the lower (negative frequency) bandedge signal. As such, an all digital solution to timing recovery from a VSB signal for a high definition television is provided.